The long-term goal of this project is to understand the diversity of reproductive proteins and the functional consequences of their divergence, which could involve problems in fertility and speciation due to a mismatch of sperm-egg recognition molecules. A recurring observation in the study of reproductive proteins is their rapid, adaptive evolution. This phenomenon occurs in organisms diverse as diatoms and mammals. The research proposed here is aimed at identifying interacting male-female reproductive proteins and studying their co-evolution in three systems: Drosophila, abalone, and mammals. [unreadable] [unreadable] Specific Aim 1 is to identify cognate male-female pairs of reproductive proteins in Drosophila, where no interacting male-female reproductive proteins are known. This will greatly increase the use of Drosophila as a model organism for the study of reproductive proteins. [unreadable] [unreadable] Specific Aim 2 is to use abalone to test the functional consequences of diversity in reproductive proteins using a well-established interaction of sperm and egg molecules. This is not currently possible in other animal systems. Specific Aim 3 uses the knowledge gained from the study of reproductive protein diversity in other systems to test for correlated changes in sperm-egg recognition molecules from a pool of proposed interacting mammalian sperm-egg molecules. The identification of interacting mammalian sperm-egg molecules is a long-standing controversy in mammalian fertilization. Our approach, a direct application of results and ideas from basic research, is a novel comparative genomics analysis aimed at testing the proposed interactions. [unreadable] [unreadable]